DESCRIPTION (Applicant's abstract verbatim): Each year in the USA, more than 500,000 patients are hospitalized with venous thrombosis (VT) and pulmonary embolism (PE). Of these patients, nearly 200,000 die. Despite the magnificent advances in imaging techniques, diagnosis of VT and PE continues to be challenging. Because scintigraphic imaging technique is simple, non-invasive, and permits rapid scanning of the entire body, the FDA has recently approved Tc-99m-AcuTect for imaging clots. AcuTect, however, can neither image old clots nor detect most PE. Fibrin is a major, integral part of VT, fresh or old, as well as of PE. During our NIH Phase I study we have developed Tc-99m-fibrin specific peptide, with which in vitro and in vivo imaging results are promising. Our primary goals in the Phase II studies are to evaluate the ability of this agent (Tc-99m/ TP 850) i) to image up to 96 hr old VT and PE, ii) to compare the efficacy of Tc-99m-TP 850 with Tc 99m-AcuTect to image VT and PE, iii) to examine the efficacy of Tc-99m-TP 850 to image fresh and old VT and PE treated in vivo with anticoagulating agent heparin, and iv) to perform pharmacokinetics and radiation dosimetry studies in 10 healthy human volunteers. We believe that the results of these studies will allow us to determine the full potential of Tc-99m-TP 850 and permit us to rapidly initiate clinical trials. PROPOSED COMMERCIAL APPLICATIONS: Following the proposed evaluation in swine and Phase I studies in humans, the agent should be ready to be examined in patients with DVT and PE. Because there are no agents currently available than can scintigraphically provide "hot spot" images of old (24 hr or older) clots and PE, the commercial potential for this agent is very high.